May the Force (Field) Be with You

If astronauts hope to ever set foot on Mars, myriad technical challenges will need to be overcome, not the least of which is shielding space travelers from bombardment by energetic particles. Outside Earth's protective atmosphere and magnetic field, supersonic particles from stellar processes run amok, screaming through space and tearing through just about anything in their path—including the bodies of astronauts, where they can wreak havoc on genetic material.

Over the years, a number of protective schemes has been proposed from physical barriers to magnetic or electrostatic shields—solutions that some prominent critics have deemed hopelessly impractical. But a group of European researchers has nonetheless taken to testing a magnetic force field approach in the laboratory, yielding results that they say show "the potential viability" of the technology.

Ruth Bamford, a physicist at Rutherford Appleton Laboratory in Didcot, England, and her colleagues fired a plasma beam of charged particles traveling above Mach 3, a stand-in for a stream of energetic solar particles, at an induced magnetic field. What they observed was an almost total deflection of charged particles around the field—a "mini magnetosphere" of relative safety, according to their study published online today by the journal Plasma Physics and Controlled Fusion.

While this strategy has long been on the table as a potential solution to the radiation problem, past approaches have deemed it untenable. As noted by Eugene N. Parker, a professor emeritus of physics at the University of Chicago, in a 2006 Scientific American article, the weight of such a system would be too great for practical space travel. Parker wrote that Nobel laureate "Samuel C. C. Ting of the Massachusetts Institute of Technology headed up a design group that devised such a system with a mass of only nine tons ... still discouragingly heavy to think of carrying all the way to the Martian surface and back."

The system Parker describes is predicated on the need to create a mammoth magnetic field of 20 teslas—some 600,000 times what one would find at the Earth's equator. Bamford is quick to caution that her team's results are preliminary, but she believes that an effective field could be much weaker, perhaps just one tesla.

The large-magnet approach, Bamford says, "is based on the assumption that you need to create a very large bubble," multiple kilometers across. "What we've been working on is the assumption that the bubble doesn't have to be that large—as small as 100 meters across," she says, "and you can get away with a much smaller magnet." This discrepancy owes in part to the fact that Bamford's team focused on solar energetic particles (those emitted from our sun) while Parker focused on cosmic-ray particles from exploding stars elsewhere in the universe.

"I was more concerned about the galactic cosmic rays, which are higher-energy, which takes therefore a stronger magnetic field," Parker says. His estimates hinge on the need to deflect particles some 20 times more energetic than those targeted by Bamford and her colleagues. The risks of those particles are not insignificant: cosmic rays would do enough damage over a year's journey through the solar system to break through a third of the DNA in an astronaut's body, according to a NASA estimate cited by Parker. (A round-trip to Mars, with current technology, would take at least that long.)

"There is still the unknown medical end of things that has not been properly investigated," Parker says, referring to the unknown effects of such long-term exposure to radiation. "And it is not obvious how to investigate it properly."

Bamford acknowledges that the magnetic field approach is not a magic bullet—more like an arrow in the quiver. Other strategies, she says, would have to be developed to minimize the risk to astronauts. But if a lightweight deflector of solar energetic particles could be developed, a trip to Mars might appear just that much less far-fetched.